@fcwilt if the relay that @reFlexlab is using is similar to that one, then he needs to connect ot to one of the IO ports, not to an OUT port. The +5V and GND pins should be connected to +5V and GND on the IO port, and the control input to the OUT pin of the IO port.
The control signal will only be 3.3V, but this will probably be enough to operate the relay.
Alternatively, use a bare relay (not a relay board) connected directly to the chosen OUT port. The relay coil should be chosen to match the VIN voltage or 12V, whichever has been selected for that OUT port.